The present invention relates generally to switches and more particularly to timer switches which are used to protect a load from the voltage irregularities of a direct current input voltage.
Many conventional loads receive power from a direct current input voltage which can be subject to voltage irregularities or excitations, such as power outages. As can be appreciated, the re-application of power to a load after the input voltage has experienced a temporary voltage irregularity can often significantly damage or destroy the load, which is highly undesirable.
Accordingly, timer switches (which are often referred to simply as timers in the art) are well known in the art and are commonly used, among other things, to protect a load from the voltage irregularities of a direct current input voltage. A timer switch can connect the load to the input voltage and suspend the re-application of power to the load after a harmful voltage irregularity in the input voltage has been experienced.
Timer switches are used in many different applications to protect various types of loads (e.g., lights, refrigerators, air conditioners, hot-swap modules, etc.) from harmful input voltage irregularities. As an example, a timer switch can be used to prevent over-stress to a HID lamp ignitor. As another example, a timer switch can be used to prevent over-stress to a system compressor while the system is still pressurized. As another example, a timer switch can be used to prevent re-application of power to hot-swap modules after a short interruption of power.
An electrical timer switch (also commonly referred to as an electro-mechanical timer switch) is one well known type of timer switch which is well known and widely used in the art. Electrical timer switches typically comprise a mechanical device, such as a thermally reactive, bi-metallic switching contact, to provide the primary switching action for the timer.
The utilization of a mechanical device to provide the primary switching action renders electrical timer switches subject to a number of significant drawbacks.
As a first drawback, it has been found that the utilization of a mechanical device to provide the primary switching action renders electrical timer switches relatively unreliable, which is highly undesirable.
As a second drawback, it has been found that the utilization of a mechanical device to provide the primary switching action renders electrical timer switches relatively large in size, which is highly undesirable.
As a third drawback, it has been found that the utilization of a mechanical device to provide the primary switching action renders electrical timer switches excessively sensitive to shock, which is highly undesirable.
As a fourth drawback, it has been found that the utilization of a mechanical device to provide the primary switching action renders electrical timer switches relatively complex in construction, which is highly undesirable.
As a fifth drawback, it has been found that the utilization of a mechanical device (i.e., an electromagnetic coil or a heating element) to provide the primary switching action causes electrical timer switches to consume (and consequently waste) a relatively large amount of energy, which is highly undesirable.
Accordingly, electronic timer switches are well known and widely used in the art. Electronic timer switches differ from electrical timer switches in that an electronic timer switch utilizes a semiconductor device to provide the primary switching action for the switch, the semiconductor device being controlled by a timing element. The utilization of the semiconductor device is desirable when the electronic timer switch has a definitive snap, or hysteretic, switching action, thereby eliminating the occurrence of an intermediate switching state which may result in damage to or unstable operation of the timer switch and load. An example of such an electronic timer switch which utilizes a semiconductor device to provide the primary switching action for the switch is manufactured and sold by Philips Semiconductors under the model number NE555.
As can be appreciated, electronic timer switches experience a number of significant advantages over electro-mechanical timer switches.
As a first advantage, electronic timer switches are more reliable than electro-mechanical timer switches.
As a second advantage, electronic timer switches are smaller and less expensive than electro-mechanical timer switches.
As a third advantage, electronic timer switches are less sensitive to shock than electro-mechanical timer switches.
Although well known and widely used in commerce, electronic timer switches of the type described above often suffer from a couple notable drawbacks.
As a first drawback, electronic timer switches typically require a constant application of voltage from a power supply, which is highly undesirable.
As a second drawback, electronic timer switches typically comprise a timing element which includes a plurality of energy storage elements, such as capacitors. As can be appreciated, the utilization of a plurality of energy storage elements significantly increases the size and cost of the switch, which is highly undesirable. In addition, the utilization of a plurality of energy storage elements renders the switch less reliable, which is highly undesirable.
It should be noted that particular voltage irregularities are often experienced by the input voltage which are not considered harmful to the load. As a result, electronic timer switches are often constructed to include one or more features which permit the re-application of power to the load after the occurrence of one of such harmless voltage irregularities.
As an example, an anti-short cycle timer switch often includes a switch-bounce immunity feature. A switch-bounce immunity feature allows for the re-application of power to the load after a voltage irregularity if the voltage irregularity occurs before the input voltage has been continuously applied to the load for a time period which is less than the time constant for the timer switch. As a result, a timer switch which includes a switch-bounce immunity feature does not interrupt power to the load during the short time period after initial application of power to the switch in which timer switches are prone to harmless initial power switch bouncing.
As another example, a timer switch often includes a latching feature. A latching feature allows for the re-application of power to the load if the application of power has been withdrawn from the load by the switch for a time period which is greater than the time constant for the switch (e.g., a lengthy power outage).
As another example, a timer switch often includes an auto-resetting feature. An auto-resetting feature allows for the automatic re-application of power to the load if the timing element of the timer switch experiences a significant cool-down, or discharge, time period which is greater than the time constant of the switch.
It is an object of the present invention to provide a new timer switch.
It is another object of the present invention to provide a new electronic timer switch.
It is yet another object of the present invention to provide an electronic timer switch which does not require a constant application of voltage from a power supply.
It is still another object of the present invention to provide an electronic timer switch as described above which includes a limited number of energy storage elements.
It is yet still another object of the present invention to provide an electronic timer switch which is immune to switch-bouncing.
It is another object of the present invention to provide an electronic timer switch which is highly reliable and which is relatively insensitive to shock.
It is yet another object of the present invention to provide an electronic timer switch which has a limited number of parts, which is relatively small in size, which is easy to use, and which is inexpensive to manufacture.
Accordingly, there is provided a timer switch for protecting a load from the voltage irregularities of an input voltage, the load having a first terminal and a second terminal, the second terminal of the load being connected to ground, said switch comprising a transistor switch which includes a first terminal, a second terminal and a third terminal, the first terminal of said transistor switch being connected to the input voltage and the third terminal of said transistor switch being connected to the first terminal of the load and an energy storage element which includes a first terminal and a second terminal, the first terminal of said energy storage element being connected to the second terminal of said transistor switch and the second terminal of said energy storage element being connected to ground.